The present invention relates generally to cut-sheet handling equipment and more specifically to a method of using automatic size sensors in the document input feeder of a scanner, copier, or similar image forming system adapted to handle documents of varying sizes. It is believed that the technology also has general applicability to package handling and other article handling equipment.
In many imaging systems that input documents of varying sizes such as scanners, copiers, and fax systems, it is necessary or desirable that the machine obtain information regarding the size of the input documents. For instance, both U.S. Pat. No. 4,669,863 issued to Yoshiura et al. and U.S. Pat. No. 5,150,224 issued to Mizude et al. disclose systems that coordinate size-selection of copy substrates with the size of input documents and of the amount of image magnification, if any, used in the job. Additionally, most current printers and copiers with multiple output bins provide that one bin is selected as a default such that in the absence of a specific alternate selection by the operator, substrates from that bin are fed into the printer or copier for imaging. If input documents are of different size from the default substrate, then the printed image is often cropped or, alternatively, too small for the output substrate. It would be advantageous if the substrate bin default selection was automatically adjusted to select the bin with the substrate size that most closely corresponds in size to the input documents. Alternatively, it would be advantageous to automatically detect the size of input documents in order to adjust the amount of optical or digital magnification in order to fit the input image properly onto the selected output substrate. It would also be advantageous to automatically detect the size of input documents within the feeder apparatus rather than during image processing in order that First Copy Time Out can be reduced by commencing transport of the correct copy substrate earlier in the imaging sequence. In digital reprographic devices, it would be advantageous to rotate digital imaging information when the axis of the input documents is perpendicular to the axis of the selected copy substrate.
Prior art techniques have attempted to realize a few of the above advantages of automated document size sensing. For instance, in U.S. Pat. No. 5,150,224, issued to Mizude et al., an input document size sensor is disclosed that uses a series of light emitters and receptors located underneath a glass platen. Mizude discloses that such information about input document size can be used to compute the amount of magnification, if any, required to fit the input image onto the selected output substrate. However, as acknowledged in Mizude, such fixed arrays of a few sensors are useful in matching input document sizes to one of only a select number of standard input sizes. Irregular sizes cannot easily be determined. Moreover, the number of sensors together with the complicated wiring and logic circuits associated with techniques similar to the disclosures of Mizude lead to more costly and complicated assembly procedures and to less reliability. See also U.S. Pat. No. 4,908,672, issued to Ito, where an unspecified document size sensor is used to help select magnification and a preferred selection of copy substrates.
More attention has been devoted in the prior art to techniques for automatically detecting the size of copy substrates loaded in one or more copy substrate paper trays. In U.S. Pat. No. 5,290,225, issued to Saito, substrate length is detected by measuring the travel time from lead to trailing edge of the substrate as it is transported from the paper tray to the imaging station. In both U.S. Pat. No. 5,328,166, issued to Hokamura, and U.S. Pat. No. 5,188,351, issued to Gysling, apparatus is disclosed for automatically detecting the size of paper loaded into a removable paper cassette by detecting the position of an adjustable paper guide. In Hokamura, sensors are disposed on the printer underneath the removable cassette such that they detect the position of the paper guide(s) in order that the printer processor can determine which of several predetermined sizes are loaded. See also U.S. Pat. No. 5,110,106 issued to Matsumura et al. In Gysling, a cam-operated shaft is moved up or down in response to position shifts of the paper guide(s). An electrically active wiper blade is attached to the movable end of the shaft such that shifts in the shaft position trigger result in electrical connections with one of a series of electrical detectors.
In U.S. Pat. No. 5,360,207, issued to Rauen et al., six embodiments are disclosed that are directed toward coupling of a substrate paper guide to a linear or rotary encoder or potentiometer. As a paper guide is manually nudged against a stack of copy substrates, its position is converted by the encoder or potentiometer into a signal indicative of that position. A processor then converts the signal into a read-out of the paper size. As explained in Rauen, information concerning the size of copy substrates can be used to maximize system throughput by enabling improved pitch control and by enabling instructions to be given that direct the operator to re-orient copy substrates into the direction that will maximize system throughput. Although the invention of Rauen has been known in the art for a number of years, it is believed that the invention has not been used in a commercial device. The reasons for this lack of use appear to be the relatively high cost of linear encoder apparatus suitable for commercial use and, for less expensive variable resistance potentiometers, inconsistent readings due to variations with temperature, variations between units, and variations over time as parts wear.
In U.S. Pat. No. 4,585,332, issued to Shenoy, a paper tray with as few as three fixed sensors is disclosed. That patent teaches that the number of different size sheets that can be detected is N+2, where "N" stands for the number of sensors.
Relevant portions of each of the above references are hereby incorporated by reference. None of these references, however, disclose apparatus for automatically detecting many sizes of sheets using only a few reliable and inexpensive components. Also, none of the above references disclose methods by which an image forming device may use automatically generated document size data to improve system throughput, automatically select copy substrates, and enhance image processing for input documents.